The Olympic and Paralympic track star's defense has argued Reeva Steenkamp was first hit in the head and could not have continued to scream in the early hours of Valentine's Day 2013, when she was killed at his luxury Pretoria home.
Pistorius has pleaded not guilty to the premeditated murder of the 29-year-old model and law graduate, saying he shot her through the toilet door in a tragic accident, having mistaken her for an intruder.
Prosecutors are seeking to prove that Pistorius fired four rounds through the door from a 9 mm pistol, in a deliberate attempt to kill. If found guilty of murder, he faces a minimum of 25 years behind bars.
Police ballistics expert Christian Mangena said he believed Steenkamp had been standing behind the door when the first bullet struck her hip, causing her to fall down on top of a magazine rack next to the toilet seat.
He said she was most likely seated in a defensive position by the time the final bullet hit her in the head. "Reeva must have had both hands covering her head protectively," Mangena testified.
"The last bullet hit her on the head, breaking the skull."
The court also saw grisly pictures of the blood-spattered toilet.
Mangena's testimony is consistent with that of previous witnesses, who said they heard screams from a woman before and during a burst of gunshots.
The first witness at the trial, Pistorius' neighbor Michelle Burger, testified to having heard "bloodcurdling screams" before four shots went off in the early hours of February 14. She also said the screams began to fade after the final shot.
Pistorius' lower legs were amputated as a baby but he went on to achieve global fame as the "fastest man on no legs," running on carbon-fiber prosthetic limbs to win gold medals at the Beijing and London Paralympics.
Nicknamed the "Blade Runner", he also reached the 400 meters semi-finals at the London 2012 Olympics, competing against able-bodied athletes.
After reconstructing the murder scene, firing several rounds of bullets from different heights and positions, Mangena concluded Pistorius was not on his prosthetics when he fired the shots.
In an affidavit in his bail hearing last year, Pistorius testified he felt especially vulnerable because he was on his stumps when he thought an intruder had entered his home.
South Africa has one of the world's highest crime rates and violent break-ins are common. However, the state has attempted to portray Pistorius as short-tempered and obsessed by guns.
Prosecutor Gerrie Nel told the court that the state would be ready to rest its case next week, earlier than experts had anticipated and setting up the defense to call Pistorius as a witness.
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